5.3.1 FHIR Resources for Ordering Laboratory Tests

When ordering laboratory tests, FHIR provides specific resources to support this process. This page outlines the key FHIR resources involved in ordering laboratory tests, focusing on how SNOMED CT and/or LOINC can be bound to these resources to ensure standardized and accurate documentation within electronic health records (EHRs) and other clinical systems. These resources help ensure that lab test orders are transmitted, processed, and documented consistently across different healthcare systems.

The diagram below illustrates how the integration of SNOMED CT and LOINC can be utilized in laboratory test ordering and processing, using FHIR ServiceRequest to support interoperability between SNOMED CT-enabled Electronic Health Records (EHRs) and LOINC-enabled Laboratory Information Systems (LIS).

In this process, a laboratory test request is encoded using SNOMED CT within the EHR system. If needed, the corresponding LOINC code is derived using the LOINC Ontology. The request is then transmitted via FHIR ServiceRequest, containing either the SNOMED CT concept alone or both the SNOMED CT concept and its corresponding LOINC code.

On the receiving end, if only the SNOMED CT concept is provided, the LIS derives the appropriate LOINC code using the LOINC Ontology. The laboratory system then identifies and processes the request based on LOINC.

FHIR Service Request Resource

The FHIR ServiceRequest resource is used to represent a request for a service to be performed, such as laboratory tests, imaging studies, or procedures. It facilitates standardized communication between healthcare systems, ensuring that test orders and service requests are accurately transmitted and processed.

In the context of laboratory test ordering, the ServiceRequest.code element is used to specify the requested test. This field can contain either a SNOMED CT code, a LOINC code, or both, depending on how the ordering system captures and transmits test requests.

• When SNOMED CT is used, the code element holds the SNOMED CT concept representing the requested test.
• When LOINC is used, the code element contains the appropriate LOINC code that corresponds to the requested laboratory test.
• In cases where both SNOMED CT and LOINC are included, SNOMED CT provides a structured clinical representation, while LOINC ensures compatibility with laboratory systems that primarily use LOINC for test identification.

By supporting both SNOMED CT and LOINC within the ServiceRequest.code element, FHIR enables flexible and interoperable test ordering workflows, ensuring accurate and efficient exchange of laboratory test requests across healthcare systems.

Terminology Binding

Example

Below is an example of a FHIR ServiceRequest resource that uses both the SNOMED CT concept 72641010000107 |Arbitrary concentration of antibody to hepatitis E virus in serum at point in time (observable entity)| and the associated LOINC code 51459-6 for a request to measure the arbitrary concentration of antibodies to hepatitis E virus in serum:

{
  "resourceType": "ServiceRequest",
  "id": "service-request-hev-antibody-test",
  "status": "active",
  "intent": "order",
  "priority": "routine",
  "code": {
    "coding": [
      {
        "system": "http://snomed.info/sct",
        "code": "72641010000107",
        "display": "Arbitrary concentration of Hepatitis E virus antibody in serum at point in time by immunoassay (observable entity)"
      },
      {
        "system": "http://loinc.org",
        "code": "49776-8",
        "display": "Hepatitis E virus Ab [Units/volume] in Serum by Immunoassay"
      }     
    ],
    "text": "Hepatitis E Virus Antibody Concentration Test"
  },
  "subject": {
    "reference": "Patient/example",
    "display": "John Doe"
  },
  "authoredOn": "2025-01-28",
  "requester": {
    "reference": "Practitioner/example",
    "display": "Dr. Smith"
  },
  "performer": [
    {
      "reference": "Organization/lab-example",
      "display": "Example Diagnostic Laboratory"
    }
  ],
  "specimen": [
    {
      "reference": "Specimen/example-serum",
      "display": "Serum Sample"
    }
  ],
  "note": [
    {
      "authorString": "Dr. Smith",
      "time": "2025-01-28T10:00:00Z",
      "text": "Please measure the concentration of antibodies to hepatitis E virus."
    }
  ]
}

Explanation:

• status: Set to “active,” indicating that the request is currently in progress.
• intent: “order” reflects that this is a formal request.
• code:
  • coding: Uses the SNOMED CT conceptId 72641010000107
  • coding: Uses the LOINC code 51459-6
• subject: Refers to the patient for whom the test is being ordered.
• requester: Indicates the practitioner making the request.
• performer: Specifies the organization or laboratory that will perform the test.
• specimen: Points to the serum sample to be tested.
• note: Includes additional instructions or details related to the test.

By leveraging the LOINC Ontology, it is possible to automatically derive the corresponding LOINC code for the SNOMED CT concept 72641010000107 |Arbitrary concentration of antibody to hepatitis E virus in serum at point in time (observable entity)|, see image below. The corresponding LOINC code is 51459-6, which represents the same clinical concept in the LOINC terminology system.